The gene analysis is recently paid an attention in developing gene technology.
For the gene analysis, microarray is now widely employed. The microarray has a number of areas in each of which probe molecules such as nucleic acid fragments are placed. Sample DNA fragments obtained directly or via PCR technique from the target genes are labeled with fluorescent label and then brought into contact with the probe molecules on the microarrays. When the sample DNA fragments are complementary to the probe molecules on the microarray, hybridization occurs so that the sample DNA fragments are combined with the probe molecules, to form hybrid structures on the microarray. Thus formed hybrid structures can be locating by detecting the fluorescent label of the combined target DNA fragments.
The microarray is particularly useful for the purpose of gene expression analysis.
For instance, Patrick O. Brown & David Botstein describe in “Exploring the new world of the genome with DNP microarrays” (Nature Genetics Supplement, Vol. 21, January 1999, pp. 33-37), differential hybridization using different fluorescent labels. In the differential hybridization procedure, one of different fluorescent labels is attached to DNA fragments in one sample, while another fluorescent label is attached to DNA fragments in another sample. Both samples are spotted on a microarray for performing hybridization to form hybrid structures. The positions of thus formed hybrid structures are located by detecting each of fluorescent labels of the hybrid structures on the microarray. The detected data are compared with each other to analyze difference between DNA composition of one sample and DNA composition of another sample.
U.S. Pat. No. 5,800,992 describes a method for detecting nucleic acid sequence in two or more collections of nucleic acid molecules. The method comprises (a) providing a microarray having polynucleotides comprising determinable nucleic acid; (b) contacting the array with (i) a first collection of labelled nucleic acid comprising a sequence substantially complementary to a nucleic acid of the array, and (ii) at least a second collection of labelled nucleic acid comprising a sequence substantially complementary to a nucleic acid of the array, wherein the first and second labels are distinguishable from each other; and (c) detecting hybridization of the first and second labelled complementary nucleic acids to nucleic acids of the arrays.
Electrochemical detection of DNA fragments using a electroconductive microarray having an array of electrodes on which probe molecules of DNA fragment is disclosed in U.S. Pat. Nos. 4,840,893 and 5,776,672.
P. E. Nielsen et al., Science, 254, 1497-1500(1991) and P. E. Nielsen et al., Biochemistry, 36, pp. 5072-5077 (1997) describe PNA (Peptide Nucleic Acid or Polyamide Nucleic Acid) which has no negative charge and functions in the same manner as DNA does. PNA has a polyamide skeleton of N-(2-aminoethyl)glycine units and has neither glucose units nor phosphate groups.
Since PNA is electrically neutral and is not charged in the absence of an electrolytic salt, PNA is able to hybridize with a complementary nucleic acid to form a hybrid structure which is more stable than hybrid given by a DNA prove and its complementary nucleic acid (Pre-print of the 74th Spring Conference of Japan Chemical Society, pp. 1287, reported by Naomi Sugimoto).
The aforementioned P. E. Nielsen et al., Science, 254, 1497-1500(1991) also describes a PNA probe labelled with isotope element and a detection method of a complementary nucleic acid.